Kwangin Kim

Fuel cell based on novel hyper-branched polybenzimidazole membrane

AbstractA novel hyper-branched polybenzimidazole (HB-PBI) has been synthesized and efficiently utilized as a conducting polymer for the fabrication of an efficient high temperature fuel cell. The developed fuel cell showed outstanding proton conductivity (0.168 Scm−1 at 150 °C) along with excellent single cell performance, displaying a maximum power density of 0.346 Wcm−2. The HB-PBI has been synthesized by polymerization of bibenzimidazole diterephthalic acid (BBIDTA) and 3,3′-diaminobenzene in the presence of poly phosphoric acid while the BBIDTA was synthesized by treating trimellitic anhydride with 3,3′-diaminobenzene. Both HB-PBI and BBIDTA were structurally characterized by nuclear magnetic resonance (1H and 13C NMR). HB-PBI showed high thermal stability and mechanical properties, findings that were corroborated by thermogravimetric analysis and use of a universal testing machine. Additionally, proton conduction and the thermal and mechanical properties of HB-PBI were compared with polybenzene imidazole (m-PBI), and found that HB-PBI has higher proton conducting, thermal and mechanical properties.

Synthesis, characterization, and thermal and proton conductivity evaluation of 2,5-polybenzimidazole composite membranes

In this contribution, composite membranes (CM-D and CM-S) of 2,5-polybenzimidazole (PBI) were synthesized by adding inorganic heteropoly acids (IHA-D and IHA-S). IHA-D and IHA-S were synthesized by condensation reaction of silicotungstic acid with tetraethyl orthosilicate (TEOS) in the absence and presence of mesoporous silica (SiO2), respectively. The synthesized composites were structurally and morphologically characterized and further investigated the functional relationships between the materials structure and proton conductivity. The proton conductivity as well as thermal stability was found to be higher for composite membranes which suggest that both properties are highly contingent on mesoporous silica. The composite membrane with mesoporous silica shows high thermal properties and proton conductivity. IHA-D shows proton conductivity of almost 1.48 × 10-1 Scm-1 while IHA-S exhibited 2.06 × 10-1 Scm-1 in nonhumidity imposing condition (150°C) which is higher than pure PBI. Thus introduction of inorganic heteropoly acid to PBI is functionally preferable as it results in increase of ion conductivity of PBI and can be better candidates for high temperature PEMFC.

Effects of nanoclay on the properties of low temperature cured polyimide system

Polyimide is a major polymer material in the electronics industry, and we conducted a study to cure polyimide at low temperatures in order to improve its thermal and mechanical properties. In this study, polyimide/clay nanocomposites were prepared by the reaction of 4,4’-(hexafluoro isopropylidene) diphthalic anhydride (6FDA) and 4,4’-oxydianiline (ODA) with the addition of 1,4-dizabicyclo[2.2.2]octane (DABCO) as a low-temperature catalyst and nanoclay (Cloisite 20A). The synthesis of polyimide at low temperatures and the dispersion of a nanoclay in the polymer matrix was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. Thermal stabilities of the nanocomposites were confirmed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The mechanical properties were measured by an universal testing machine. We demonstrated that when polyimide was cured at low temperatures and short curing times, it was possible to improve the thermal and mechanical properties via the addition of a catalyst and inorganic material. Polyimide with DABCO and 0.25 wt% nanoclay showed a 5 °C higher degradation temperature, 560.88 °C; a 6 °C higher glass transition temperature, 293.62 °C; and a 20 MPa greater tensile strength, 136.94 MPa. Therefore, the polyimide curing process was demonstrated to be successful at low temperatures.

Synthesis of a new diamine and its effect on the residual stress of colorless polyimide

A new diamine was designed and synthesized to improve the flexibility of colorless polyimides by reducing residual stress. Four variations of colorless polyimides with the same dianhydride (4,4′-(hexafluoroisopropylidene)-diphthalic) and four different diamines (bis[4-(3-aminophenoxy)-phenyl] sulfone, bis(3-aminophenyl) sulfone, 2,2′-bis(trifluoromethyl)benzidine, and 2,2-bis(4-aminophenyl)-hexafluoropropane) were used. A series of colorless polyimides were prepared by adding the new diamine. The carbon and ether bonds between the benzene rings of the new diamine affected the flexibility and optical properties of colorless polyimide. The synthesis of the new diamine was confirmed by NMR measurements. Furthermore, the decrease in residual stress at room temperature and the glass transition temperature was confirmed. The effect of the new diamine was most evident for polyimide with a bulky and rigid structure. Though a slight yellow color appears because of the broken charge transfer complex balance, controlling the content of the new diamine will allow application of polyimides in flexible display.

Norbornene end-capped polyimide for low CTE and low residual stress with changes in the diamine linkages

AbstractThe effects of norbornene (NE) crosslinking and diamine bridge linkages (ether, sulfone, and trifluoromethyl) on polyimide films were investigated. The purpose of this study was to study the behavior of the NE endcapped polyimide with different diamine bridge linkage structure at elevated temperatures on residual stress and modulus change. 5-Norbornene-2,3-dicarboxylic acid was introduced as the end-capping agent in order to increase the ratio of crosslinking in the structure through reverse Diels-Alder reaction. Wide angle X-ray diffraction (WAXD) was measured to study the relation of d-spacing and structure change of the bridge linkage of polymers through NE crosslinking. Coefficient of thermal expansion (CTE) and residual stress were measured to confirm the loaded stress between the substrate and polymer film through a thin film stress analyzer (TFSA). Storage (ε′) and loss modulus (ε″) were studied at elevated temperatures to study the relation of bridge linkage mobility of the polyimide at elevated temperature.

Erratum to: Low dielectric transparent poly(amide-imide) thin film with nano scale porous structure

Page 1115, the Acknowledgments should be corrected as follows:This work was supported by the KIST Institutional Program (Project No. 2E26600-16-041) and National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2017R1D1A1B03033332).

Solventless UV Curable Material for Low Cost System

Received 13 December, 2016 Revised 24 February, 2017 Accepted 28 February, 2017 Abstract >> In this study, Poly-urethane acrylate (PUA) was synthesized by the reaction between Polycaprolactonetriol (PCLT) and Isophorone dissocyanate (IPDI) and hybridized with inorganic materials. Tetraethylortho silicate (TEOS) and nano clay (Closite 20A) were used as inorganic particles. For the hybridization of TEOS with PUA, sol-gel method is used, in which TEOS is made into spherical particle in the firsthand. In the case of Nano clay, hybridization is carried out through the dispersion as Nano clay has a layered structure. The solution of PUA hybrid was made into a film after UV curing and its thermo and electrical properties were measured. The experimental analysis and result demonstrate that the PUA hybrid shows an improved thermal properties and lower dielectric constant than that of the non-hybrid PUA. The trend of improved properties was different depending on structure of inorganic materials.

Low dielectric transparent poly(amide-imide) thin film with nano scale porous structure

AbstractA transparent poly(amide-imide) (PAI) was synthesized with good thermal and optical properties and after that silica nano particles were introduced and removed for nano porous polymer matrix. The successful synthesis of PAI with nano scale porous structure was confirmed with FT-IR and FE-SEM measurement. The effects of free volume of polymer on thermal properties were measured with TGA and DSC. This physically modified polymer matrix showed increased thermal degradation and glass transition temperature over 250 °C. In the case of optical properties, UV-Vis and yellow index were measured and PAI with nano porous structure showed transparent colorless properties with light transmittance in the range of 80-40% and yellow index 2.1-1.1. The results also showed low dielectric constant in the range of 3.2-2.5 and contact angles that of 70-73°.